Television receiver



TELVIS ION RECEIVER original Filed Jan. 21, 1935 ra Flaw/v4 COA/790A 'H/wey Patented Dec. 31, 1940 UNITEDV STATES 1 `".liELltyrsIoiv RECEIVER Kurt Schlesinger, Berln, Germany, assignor, by

mcsne assignments, `to Loewe Radio, Inc., a corc .poration of NewYork Original application January 21, 1935, Serial No. 2,631. Divided and this application October 22, 1935, Serial No. 46,124. In Germany January z claims. lol. iis-#7.3)

The subject matter of this application is a method of and apparatus for` thepwireless synchronisation of television transmission and is a division of my application Serialy No. 2,631 filed Jan. 21, 1935, since issued as United States Letters Patent No. 2,173,495. In this connection synchronisation impulsesare transmitted simultaneously with the image current frequenciesfin the form of mixed frequencies. These frequen` cies call for separation at the receiver.

The synchronisation impulses are produced at the transmission end as black impulses, i. e., impulses which may interrupt the aerial current for ya brief space of time, of which impulses, in the manner known per se, a group of the duration of approximately 5% of the length of an image line or less serve for synchronising the commencement of the line, whilst a group of impulses,vthe duration of which corresponds to several lines, cause the synchronism in the change 'ofimage In accordance with the invention, the signals are transmitted as black signals, as in this manner there is also accomplished simultaneously a darkening of the return lines otherwise inter` fering with the image.

The drawing shows schematically circuits by which the invention may be practised. In the drawing, Fig. 1 is a circuit wherein combined picture and synchronizing signals are received and separated; and Fig. 2 represents in further schematic form a modification of the circuit of Fig. l.

In the receiving rectifier 22 the synchronizing impulses make themselves apparent in the form of a negative peak-potential at the lead 29 leading to the image reproducing device. The impulses are, therefore, separated from the image current, the peak potentials of which they exceed, by a filter valve 30.

In the lead 29 connected to the output of the receiving amplier the synchronizing impulses appear, as is well known, next with the image point impulses representative of the light and shade values of the picture. Separation of the signals is performed on account of the different frequency by means of a'filter including a condenser 32 and a resistor 33, the condenser 32 being, for example, of the order of 0.002 mf. and the resistor 33 being of the order of 8,000 ohms, so that only image-change impulses lasting for approximately one milli-second and shorter periods reach the cathode 3| of the tube 30, while the lower frequencies are not transmitted. The tube which may .be suitably biased, is preferably a gas-filled diode with a hot cathode formers, 34 and 35, which are serially. connected, l

receive the output from the tube 30. Trans,- former 34 is preferably tuned to the chosen high frequency which may be of the order of 100,000 cycles and mayhave a primary Winding of 400 turns and a secondary winding of 200 turns.

VThis transformer is preferably connected with suitable screening means and a center feed, as shown. The secondary transformer is so polarized or wound that the line frequency impulses reachthe terminal 48 with positive sign. The same eifect is performed with respect to the lower frequency (line frequency) impulses by the iron transformer`35, which may have a winding of the order of 6,000 to 18,000. -The secondary of the transformer 35 is connected over a low pass filter comprising resistor 4l and condenser 42, to a terminal point 43. The resistor 4I may be of the order of .2 megohms and a capacity of the order of 0.01 mf. The terminal points 48 and 43 are then connected with the scanning apparatus or relaxation oscillator for the television received.

It has been found in practice that proper operation of the superheterodyne on the same chassis as that used for the amplitude filter circuit was very diiicult, if not impossible, because from the ultra short wave local oscillator which is provided in the high frequency amplier portion remnant ultra high frequency oscillations pass to the body of the chassis, which may be considered as ground for the receiver. This difculty is overcome and a remedy obtained by the use of positive chokes 44 and 45 for ultra high frequency. The chokes 44 and 45 are preferably mounted or positioned in the leads conducting the synchronising impulses which are passing through the wall of the chassis so that the operation of the lead within the chassis up to the choke is as shown. f

Simultaneously the direct current included in the impulse signal is employed according to the invention for regulating the degree of amplification of the receiver. This effect is obtained in practice by means of a resistance capacity combination comprising the parallelly connected resistor 46, which may be of the order of 0.5 megohms, and the capacity '41, which may be of the `order of 0.001 mf. in series with the transformers 34 and 35. The time constant of the circuit, including the resistor 46 and capacity 41, should preferably be of the order of the image repetition rate, (for example 1/5 second) so that the fading regulation which is obtained from the voltage appearing at the terminal point 40 operates sufficiently rapidly to hold the amplification level as desired. The resistor 46 should also be selected soV as to be large as compared to the internal resistor of the tube and the resistor In the modified form of arrangement shown by' Fig. 2, the transformers 34 and 35 maybe replaced where desired, by two parallel auto-trans7 formers 38 and 39. These transformers may be tuned by means of condensers 5I, 52 to the basic frequencies of the line and frame 'synchronizing impulses and connected toground at the mid points.

appearing in the lead 29, which is originally preferably negative and converted into a positive signa The novel featureswhich I believe to be characteristic of myinvention are set forth with particularity in the appended claims. r

I claim: l

1. A television receiver of the superheterodyne `type including an amplier for receiving picture signals and both line and frame synchronizingl signals, wherein the synchronizing signals are each of a polarity representing black in the picture and -of a different duration for line and frame, an'd said" synchronizing signals are of greater amplitude in the black direction than any picture signals, lter means connected in the output circuit of the amplier for separating the synchronizing signals from the picture signals, a pair of transformers connected in the output of the filter means for separating the line and frame synchronizing signals'one from the other,v one of said transformers being tuned to the line frequency synchronizing signals and the other tuned This connection also provides the desired reversal of phase of the synchronizing impulses.

to the frame synchronizing signals, oscillation generating means connected to receive the separated synchronizing output energy from the transformers, and a high frequency choke coil connected serially intermediate each transformer output and the oscillation generator means for preventing Aheterodyne frequency energy from reaching the oscillation generating means, said transformers and choke coils being within a common shield.

2. A television receiver of the superheterodyne type including an amplifier for receiving picture signals and both line and frame synchronizing signals, wherein the synchronizing signals are Y eachof a polarity representing black in the picture and of adfferent duration for line and frame,`and`y said Ysynchronizing signals are of greater amplitude .in the black direction than any picture signals, lter means connected in the output circuit of the amplifier for separating the synchronizing signals from the picture signals, a pair of transformers serially connected Vin the output of the filter means for separating the line and frame synchronizing 'signals one from the other, one of said transformers being tuned to the line frequency synchronizing signalsv and 'the' 

